Actuated leg prosthesis for above-knee amputees

ABSTRACT

The actuated leg prosthesis comprises a knee member, a socket connector provided over the knee member, an elongated trans-tibial member having a bottom end under which is connected an artificial foot, and a linear actuator. A first pivot assembly allows to operatively connect the trans-tibial member to the knee member. A second pivot assembly allows to operatively connect an upper end of the actuator to the knee member. A third pivot assembly allows to operatively connect a bottom end of the actuator to the bottom end of the trans-tibial member. The prosthesis can be provided as either a front actuator configuration or a rear actuator configuration.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefits of U.S. provisionalpatent applications No. 60/405,281 filed Aug. 22, 2002; No. 60/424,261filed Nov. 6, 2002; and No. 60/453,556 filed Mar. 11, 2003, all of whichare hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present invention relates to an actuated leg prosthesis forabove-knee amputees.

BACKGROUND

[0003] Over the years, many kinds of leg prostheses have been devised ineffort to replace the leg or legs that amputees have lost. All these legprostheses have the difficult task of giving to these amputees a life asnormal as possible. The complexity of human locomotion, however, is suchthat conventional leg prostheses have until now only been using passivemechanisms in the most sophisticated available devices. Conventional legprostheses are very limited compared to a real human leg and some needswere thus not entirely fulfilled by them.

[0004] According to amputees, specific conditions of use of conventionalleg prostheses, such as repetitive movements and continuous loading,typically entail problems such as increases in metabolic energyexpenditures, increases of socket pressure, limitations of locomotionspeeds, discrepancies in the locomotion movements, disruptions ofpostural balance, disruptions of the pelvis-spinal column alignment, andincreases in the use of postural clinical rehabilitation programs.

[0005] Another problem is that during the amputees' locomotion, energyused for moving the prosthesis mainly originates from the amputeesthemselves because conventional leg prostheses do not haveself-propulsion capabilities. This has considerable short and long-termnegative side effects. Recent developments in the field of energy-savingprosthetic components have partially contributed to improve energytransfer between the amputees and their prosthesis. Nevertheless, theproblem of energy expenditure is still not fully resolved and remains amajor concern.

[0006] A further problem is that the dynamic role played by the stumpduring the amputees' locomotion renders difficult the prolonged wearingof conventional leg prostheses. This may create, among other things,skin problems such as folliculitis, contact dermatitis, oedema, cysts,skin shearing, scarring and ulcers. Although these skin problems may bepartially alleviated by using a silicon sheath, a complete suctionsocket or powder, minimizing these skin problems remain a concern.

[0007] Considering this background, it clearly appears that there was aneed to develop improved leg prosthesis for above-knee amputees.

SUMMARY

[0008] In accordance with a first broad aspect of the present invention,there is provided an improved actuated leg prosthesis comprising a kneemember, first means for connecting a socket over the knee member, anelongated trans-tibial member, second means for connecting an artificialfoot under a bottom end of the trans-tibial member, a linear actuator,third means for operatively connecting the trans-tibial member to theknee member, fourth means for operatively connecting the upper end ofthe actuator to the knee member, and fifth means for operativelyconnecting the bottom end of the actuator to the bottom end of thetrans-tibial member.

[0009] In accordance with another broad aspect of the present invention,there is provided an improved actuated leg prosthesis comprising a kneemember, a socket connected over the knee member, an elongatedtrans-tibial member, an artificial foot connected under a bottom end ofthe trans-tibial member, and a linear actuator. A first pivot assemblyallows to operatively connect the trans-tibial member to the kneemember. The first pivot assembly defines a first pivot axis that isperpendicular to a main longitudinal axis of the trans-tibial member. Asecond pivot assembly allows to operatively connect an upper end of theactuator to the knee member. The second pivot assembly defines a secondpivot axis that is substantially parallel to the first pivot axis. Thesecond pivot axis is also spaced apart from the first pivot axis and themain longitudinal axis. A third pivot assembly allows to operativelyconnect a bottom end of the actuator to the bottom end of thetrans-tibial member. The third pivot assembly defines a third pivot axisthat is substantially parallel to and spaced apart from the first pivotaxis.

[0010] These and other aspects of the present invention are described inor apparent from the following detailed description, which descriptionis made in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

[0011]FIG. 1 is a perspective view of an actuated prosthesis with afront actuator configuration, in accordance with the preferredembodiment of the present invention.

[0012]FIG. 2 is a partially exploded perspective view of the prosthesisshown in FIG. 1.

[0013]FIG. 3 is an exploded perspective view of the knee member and thefirst pivot assembly shown in FIG. 1.

[0014]FIG. 4 is an exploded view of the trans-tibial member and thethird pivot assembly shown in FIG. 1.

[0015]FIG. 5 is a partially exploded view of the linear actuator and thesecond pivot assembly shown in FIG. 1.

[0016]FIG. 6 is a diagram illustrating the geometrical model with thefront actuator configuration.

[0017]FIG. 7 is an exploded view of the optical switch support shown inFIG. 4.

[0018]FIG. 8 is a perspective view of an actuated prosthesis with a rearactuator configuration, in accordance with another possible embodimentof the present invention.

[0019]FIG. 9 is a partially exploded perspective view of the prosthesisshown in FIG. 8.

[0020]FIG. 10 is a side view of the prosthesis shown in FIG. 8.

[0021]FIG. 11 is an exploded perspective view of the knee member, thefirst pivot assembly and the second pivot assembly shown in FIG. 8.

[0022]FIG. 12 is a partially exploded view of the trans-tibial memberand the third pivot assembly shown in FIG. 8.

[0023]FIG. 13 is a diagram illustrating the geometrical model with therear actuator configuration.

[0024]FIG. 14 is a bloc diagram showing an example of a control systemfor the actuator of the prosthesis.

DETAILED DESCRIPTION

[0025] The appended figures show an actuated prosthesis (10) inaccordance with the preferred embodiment and an alternate embodiment ofthe present invention. It should be understood that the presentinvention is not limited to these illustrated implementations sincevarious changes and modifications may be effected herein withoutdeparting from the scope of the appended claims.

[0026] The prosthesis (10) has two main configurations, one being afront actuator configuration and the other being a rear actuatorconfiguration. The front actuator configuration is preferred. FIGS. 1 to7 show the prosthesis (10) with the front actuator configuration whileFIGS. 8 to 13 show the prosthesis (10) with the rear actuatorconfiguration.

FRONT ACTUATOR CONFIGURATION

[0027]FIGS. 1 and 2 show the basic components of the prosthesis (10),which include a knee member (12), an elongated trans-tibial member (14),and a linear actuator (16) set between the knee member (12) and thetrans-tibial member (14). The prosthesis (10) also comprises means forconnecting a socket (18) on the knee member (12) and means forconnecting an artificial foot (20) under a bottom end of thetrans-tibial member (14).

[0028] The socket (18) must achieve adequate effort transfers betweenthe prosthesis (10) and the amputee's stump. The design of the socket(18) is usually a custom operation in order to achieve an optional loadtransmission, stability and efficient control for the stump's mobility.The socket (18) is generally held in place on the stump of the user by asuction effect created by an appropriate system such as, for example, aflexible suction liner of type “Thermolyn” manufactured by the Otto BockInc. The prosthesis (10) can otherwise use any suitable socketsavailable on the market.

[0029] The means for connecting the socket (18) may comprise a bottomsocket connector (22) provided over the knee member (12). The bottomsocket connector (22) is preferably removably connected by means offasteners, for instance screws or bolts. The exact type of bottom socketconnector (22) may vary. An example is a connector having a standardmale pyramid configuration, such as male pyramid model 4R54 manufacturedby Otto Bock Inc. Another example is the sliding connector with malepyramid model 2054-2 manufactured by Ossur Inc. The socket (18) wouldthen be equipped with a corresponding upper connector which fits overthe bottom male connector (22). Other types of connectors may be used aswell.

[0030] The knee member (12) ensures the junction between the socket (18)and the trans-tibial member (14) with at least one degree of freedom inrotation. The knee member (12) range of motion is preferably about 105degrees, where zero degree is at full extension and 105 degrees is atmaximal knee flexion.

[0031]FIG. 3 shows an enlarged view of the knee member (12). The kneemember (12) is preferably a fork-shaped item, with two flanges (24)projecting from an upper plate (26). The upper plate (26) includes fourthreaded holes (28) for the removable fasteners of the bottom socketconnector (22).

[0032] The knee member (12) in the preferred embodiment is connected tothe trans-tibial member (14) by means of a first pivot assembly (30).The first pivot assembly (30) allows to operatively connect thetrans-tibial member (14) to the knee member (12), thereby makingpossible a relative rotation between these two parts. It should be notedthat the first pivot assembly (30) can also be polycentric. This meansthat the movement between the knee member (12) and the trans-tibialmember (14) is not purely rotational but follows a much more complexpattern. The right and left sides of the parts can further be slightlydifferent, thereby causing a slight torsion movement around a verticalaxis. Nevertheless, the general overall movement remains substantially arotation around a pivot axis.

[0033] In the preferred embodiment, the first pivot assembly (30)defines a first pivot axis (31) that is substantially perpendicular to amain longitudinal axis (15) extending along the length of trans-tibialmember (14) in the frontal plane, as shown in FIG. 1. This first pivotassembly (30) also comprises an axle (32) supported by two bearings(34), each mounted in a corresponding housing (36) in the flanges (24)of the knee member (12). An example of bearing (34) is a singlegroove-bearing model 6300-ZZ manufactured by NSK Inc. Of course, othertypes of bearings (34) may be used as well. A 10 mm shoulder nut (37)and a set of external spacers (35) allow to retain the bearings (34) onthreaded ends of the axle (32). An optical switch support (38), shown inFIGS. 2, 4 and 7, is mounted around the axle (32) between the twoflanges (24) of the knee member (12). The support (38) is describedlater in the description.

[0034] Preferably, as best shown in FIG. 3, a set of energy absorptionbumpers (44) is provided at the back side of the knee member (12) toprevent out of range motion. These bumpers (44) can be, for example,bumper model GBA-1 manufactured by Tecspak Inc. Of course, other typesof bumpers (44) may be used as well. They are mounted on correspondingbrackets (42) located on the side and the front of the upper plate (26)of the knee member (12). The brackets (42) are also used to supportconectors (78) which are described later in the description.

[0035]FIG. 4 shows the trans-tibial member (14) in accordance with thepreferred embodiment. It includes three main sections, namely an uppersection (14A), a middle section (14B), and a bottom section (14C).

[0036] The upper section (14A) of the trans-tibial member (14) ispreferably a fork-shaped item with two flanges (50) projecting from amounting base (52). The mounting base (52) is rigidly connected to apair of trans-tibial post bars (54). A back plate (56) is provided atthe back. The pair of bars (54) and the back plate (56) are part of themiddle section (14B). They are both connected to the bottom section(14C), which is itself a two-part item in the preferred embodiment. Thefirst part (60) is a somewhat U-shaped part under which the second part(62) is attached. The second part (62) is an extension under which theartificial foot (20) is provided. The means for connecting theartificial foot (20) may comprise a set of threaded holes in whichscrews are inserted. Other types of connectors may be used.

[0037] The artificial foot (20) may be, for example, a standard 26 cmTrustep prosthetic foot manufactured by College Park Industries Inc. orAllurion model ALX5260 prosthetic foot manufactured by Ossur Inc. Othertypes of articulated or non-articulated artificial foot (20) may be usedif the selected prosthetic foot provides approximately at least the samedynamical response as the ones mentioned here above. The design of theprosthesis (10) is modular and consequently, it can be adjusted to anymorphology. The artificial foot (20) may have an exposed metal orcomposite structure. It may also have a cosmetic covering that gives itthe appearance of a human ankle and foot.

[0038] The pair of bars (54) and the back plate (56) provide a space(58) in which most of the actuator (16) is located. The variouselectronic and electric components may also be attached on either sidesof the back plate (56). This compact design allows to keep the overalldimensions within that of a normal human leg.

[0039]FIG. 5 shows the linear actuator (16) in accordance with thepreferred embodiment. The upper end (16A) of the actuator (16) isconnected to the knee member (12) and the bottom end (16B) is connectedto the bottom section (14C) of the trans-tibial member (14). Thefunction of the actuator (16) is to supply the prosthesis (10) with thenecessary mechanical energy to execute, in a sagittal plane, the angulardisplacements synchronized with the amputee's locomotion. The linearmotion of the actuator (16) is used to control the angle of the kneemember (12) with reference to the trans-tibial member (14). The actuator(16) includes an electrical motor (70) coupled with a mechanism (72, 74)to transfer rotational motion into linear motion. An example of motor(70) is the model BN2328EU manufactured by Poly-Scientific. The motor(70) operates a screw (72) engaged to a fixed follower (74) at thebottom of the actuator (16). The follower (74) is held by a followersupport (76). The follower (74) and the follower support (76) constitutethe bottom end (16B) of the actuator (16). In use, when the motor (70)rotates, the screw (72) is rotated in or out of the follower (74). Thispushes or pulls the knee member (12), thereby causing a relativerotation between the knee member (12) and the trans-tibial member (14).

[0040] The choice of the linear actuator (16) is primarily based onweight versus torque ratio and speed of available motor technologies. Itis preferred over a direct drive system coupled directly to the kneemember (12) because it takes less space for the torque requirement inhuman locomotion. It was found that ideally, the actuator (16) must becapable of supplying a continuous force of about 515 N and a peak forceof about 2250 N.

[0041] The prosthesis (10) of the preferred embodiment further comprisesa second pivot assembly (80). The second pivot assembly (80) operativelyconnects the upper end (16A) of the actuator (16) to the knee member(12). The second pivot assembly (80) defines a second pivot axis (81)that is substantially parallel to the first pivot axis (31). It is alsospaced from the plane defined by its first pivot axis (31) and the mainlongitudinal axis (15). An example of this configuration isschematically illustrated in FIG. 6. This diagram represents the variouspivot axes. The first pivot axis (31) is identified as “O”. The secondpivot axis (81) is identified with the letter “C”. Both axes (C, O) arespaced apart by the distance “r”. This distance creates a lever armallowing the actuator (16) to move the trans-tibial member (14) withreference to the knee member (12).

[0042]FIG. 5 shows that the second pivot assembly (80) of the preferredembodiment comprises a bearing (82) inserted in a mechanical connector(84) forming the upper end (16A) of the actuator (16). The bearing (82)may be a needle bearing, for example needle bearing model NK14/16manufactured by INA Inc. It is held in place by means of shoulder screws(86) and aluminum spacers (88). It was found that ideally, the bearing(82) must withstand a static charge up to about 11500 N (2600 lbf) andallows for a typical misalignment of 1 to 3°. The needle bearing (82) ispreferred since it has practically no mechanical play and a lowcoefficient of friction when compared to bushing or rod ends. Of course,other types of bearings may be used as well. An axle (90) links themechanical connector (84) to corresponding holes in the flanges (24) ofthe knee member (12). The mechanical connector (84) is secured over themotor (70) using a load cell (92), which is described later in thedescription.

[0043] The bottom end (16B) of the actuator (16) is operativelyconnected to the trans-tibial member (14) of the preferred embodimentusing a third pivot assembly (100), as shown in FIGS. 4 and 5. The thirdpivot assembly (100) defines a third pivot axis (101) and alsopreferably comprises one or more needle bearings (102), each mounted ina corresponding housing (64) provided in the first part (60) of thebottom section (14C) of the trans-tibial member (14). Two standardneedle bearings (102) may be used for that purpose, for example needlebearing model NK14/16 manufactured by INA Inc. Of course, other types ofbearings may be used as well in the second (80) and the third pivotassembly (100). A set of screws (106) and spacers (108) completes thethird pivot assembly (100).

[0044] The various structural parts of the prosthesis (10) arepreferably made of a light material, for instance aluminum or acomposite material, such as carbon fiber, fiberglass or the like. Aparticularly suitable material is thermally treated 6061T6 aluminum. Thevarious parts are preferably screwed together, although they may bewelded and otherwise secured together Screwing the parts together ispreferred since this increases manufacturability, facilitates servicingand replacement of the parts, and usually improves the overallaesthetics.

[0045]FIG. 7 shows the specialized mechanical support (38) appearing inFIGS. 2 and 4. This specialized mechanical support (38) is used firstlyto fix the optical switchs as explained hereafter. Secondly, thespecialized mechanical support (38) is used to facilitate the transitionbetween the part of a cable (not shown) between the relatively fixedsection of the prosthesis (10) and the relatively movable sectionthereof. Connectors (78), attached to the brackets (42) of the kneemember (12), provide the required connections. A similar connector (78)is provided on the motor (70). A two-part wire clamp (39A,39B) on parts(254) allows to hold the wire on the support (38).

REAR ACTUATOR CONFIGURATION

[0046] FIGS. 8 to 13 show the prosthesis (10) in accordance with asecond possible embodiment. This illustrates an example of a prosthesis(10) with a rear actuator configuration. This embodiment is very similarto the one using the front actuator configuration. It is illustratedwith another kind of actuator (16) and another model of artificial foot(20). The middle section (14B) of the trans-tibial member (14) uses fourbars (54) instead of two. It does not have a back plate. Moreover, nobottom extension is provided on the trans-tibial member (14).

[0047] The trans-tibial member (14) also has a shell type architecturecomposed, for example, of ½″ trans-tibial post bars (54) linkingtogether the knee member (12) and the artificial foot (20). In theillustrated embodiment, the actuator (16) could be a standar linearmotor (FIG. 5) or a serial elastic actuator (SEA) (FIG. 8) equipped witha customized commercially available motor (70) although the prosthesis(10) is designed such that it can receive any type of linear actuator(16) of the same approximate size. The SEA actuator (16) (FIG. 8) has aball screw transmission system including a screw (72) coupled with anelastic device (110) of known characteristics. This actuator (16) (FIG.8) allows a force control actuation based on the deformation of elasticcomponents. As well, the design allows energy storage, shock toleranceand relatively stable force control. The SEA actuator (16) (FIG. 8) wasdeveloped by Gill Pratt of the MIT Leg Laboratory and has been patentedin 1997 as U.S. Pat. No. 5,650,704. In one implementation, it wasprovided with a Litton BN23-28 motor (70) and a ⅜″ diameter with ⅛″pitch ball screw (72). The SEA actuator (16) (FIG. 8) is commercializedby Yobotic Inc.

[0048]FIG. 13 illustrates the geometrical model of the rear actuatorconfiguration. It is essentially similar to that of the front actuatorconfiguration as shown in FIG. 6.

CONTROL SYSTEM

[0049]FIG. 14 illustrates a control system (200) that can be used tooperate the actuator (16) of the prosthesis (10). This figure firstshows a set of artificial proprioceptors (210), which are sensors usedto capture information in real time about the dynamics of the amputee'slocomotion. The set of artificial proprioceptors (210) provide sensinginformation to a controller (220). The controller (220) determines thejoint trajectories and the required forces that must be applied by theactuator (16). The set-point (joint trajectories and the requiredforces) is then sent to the actuator (16) via the power drive (230)itself connected to the power supply (240).

[0050] The power supply (240) can be, for example, a flexible batterypack belt such as the Lighting Powerbelt model, manufactured by CinePower International Ltd. Other examples of power supply (240) are thebattery model SLPB526495 manufactured by Worley Inc. and the supercapacitors manufactured by Cap-XX. Examples of power drive (230) are the5121 model, manufactured by Copley Controls Corps Inc. and the modelBE40A8 manufactured by Advanced Motion Control. It should be noted thatthe design of the power supply (240) and that of the power drive (230)are not limited to the devices mentioned here above and could beperformed by any custom or commercial products if the selected devicesmeet the electrical specification of the selected actuator (16) usedwith the prosthesis (10).

[0051] Preferably, the prosthesis (10) further includes a set of sensors(250) to provide feedback information to the controller (220). Thisfeedback allows the controller (220) to adjust the forces and variousother parameters. Examples of parameters that can be monitored are therelative angle of the knee member (12) and the torque at the knee member(12) being exerted by the actuator (16). Other types of measurements maybe taken. The measurement of the relative angle of the knee member (12)can be taken, for example, by a standard commercially availableincremental optical encoder (260) such as a reading head model EM1-0-250and a Mylar® strip (262) marked with evenly spaced increments modelLIN-250-16-S2037 manufactured by US Digital Inc. Others sensors used aslimit switchs for the limitation of the angular motion of the prosthesis(10) are the optical switchs preferably mounted onto the specializedmechanical support (38). Cable connectors (78), shown in FIGS. 1 and 2,allow to link the external devices to internal components of theprosthesis (10).

[0052] The optical switches (252) are fixed on the first pivot axis (31)and are used to set the reference angular position of the knee member(12). Once this reference position is known, the optical encoderinformation is used to compute the knee member (12) angle via motorrotation, roller-screw pitch and prosthesis geometry. Moreover, theoptical switches (252) are used to prevent out of range motion bysending a signal to the controller (220) when the knee member (12)approaches critical positions. Of course, the optical switches (252) maybe use for other purposes according to the nature of the commandassociated with the switches detection. Another possible way ofmeasuring the relative angle of the knee member (12) is by using acombination of an absolute optical encoder such as, for example, encodermodel E2-512-250-I manufactured by US Digital Inc. and optical switches.An example of these switches is the switch model PM-L24 manufactured bySUNX.

[0053] The measurement of the torque is taken, for example, by astandard commercially available potentiometer measuring the compressionof the elastic devices of the actuator (16) in the rear actuatorconfiguration (FIG. 8), such as the conductive plastic resistanceelements model PTN025 manufactured by Novotechnik Inc. The force beingexerted by the actuator (16) may also be measured, as a load cell (92).An example of the load cell is the model LC 202 1K manufactured byOmegadyne. A connector on the motor (70) allows to link the internalsensor to the cable. It should be noted that the sensors (250) of theprosthesis (10) are not limited to the above-mentioned devices and canbe performed by other suitable instruments.

EXAMPLE Calculation for the Optimal Angle

[0054] One can assume the following technical specifications:

[0055] a geometrical volume corresponding to the anthropometrical volumeof a natural shank of an individual having a weight of 70 kg and aheight of 170 cm;

[0056] a maximal distance r set at 0.055 m, that is r<0.055 m;

[0057] a minimal and a maximal length L_(T) set at 0.3 m and 0.4 mrespectively, that is 0.3 m<L_(T)<0.4 m; and

[0058] a minimal and a maximal distance d_(T) set at −0.015 m and +0.015m, that is −0.015 m<d_(T)<+0.015 m.

[0059] The geometrical model can be defined with the followingequations: $\begin{matrix}{\beta = {\pi - \theta_{fix} - \alpha - \theta_{K}}} & {{Equation}\quad 1} \\{L_{A} = \sqrt{L_{T}^{2} + d_{T}^{2}}} & {{Equation}\quad 2} \\{\alpha = {\arctan \left( \frac{d_{T}}{L_{T}} \right)}} & {{Equation}\quad 3} \\{L^{2} = {L_{A}^{2} + r^{2} - {{2 \cdot L_{A} \cdot r \cdot \cos}\quad \beta}}} & {{Equation}\quad 4} \\{b_{r} = \frac{{r \cdot L_{A} \cdot \sin}\quad \beta}{\sqrt{L_{A}^{2} + r^{2} - {{2 \cdot L_{A} \cdot r \cdot \cos}\quad \beta}}}} & {{Equation}\quad 5}\end{matrix}$

[0060] where

[0061] θ_(K) Knee angle, ∠DOA

[0062] r Distance between the center of rotation “O” of the knee member(12) and the attachment point of the actuator (16) on the knee member(12)

[0063] θ_(fix) Angle between r and the stump's center axis, ∠EOC

[0064] L_(A) Distance between the center of rotation of the knee member(12) and the attachment point of the actuator (16) on the trans-tibialmember (14)^({overscore (OB)})

[0065] L_(T) Length between the center of rotation of the knee member(12) and the attachment point of the trans-tibial member(14)^({overscore (OA)})

[0066] d_(T) Distance between the center axis of the trans-tibial member(14) and the actuator (16) attachment point of the trans-tibial member(14),^({overscore (AB)})

[0067] α Angle formed between L_(T), L_(A): ∠AOB

[0068] L Length of the actuator (16),^({overscore (BC)})

[0069] β Angle formed between L_(A), r: ∠BOC

[0070] b_(r) Lever arm of the actuator (16) versus the first pivot axis(31)

[0071] Preferably, the lever arm b_(r) is assumed to be maximum at aknee angle θ_(k) of 35 degrees. The geometrical calculation of themechanical design are based on the setting of the distance r, the lengthL_(T), the distance d_(T) and the angle θ_(fix). Therefore, theseparameters are defined in accordance with the anthropomorphicmeasurements of the amputee and the selected actuator (16).

[0072] For an angle θ_(fix), the optimal value for a maximum lever armb_(r) is found when Equation 5 is at a maximum value, that is:$\begin{matrix}{\frac{\partial b_{r}}{\partial\theta_{fix}} = 0} & {{Equation}\quad 6}\end{matrix}$

[0073] where θ_(fix)=π−α−θ_(K)−β

[0074] This condition is reached for the configuration shown in FIGS. 6and 13 when: $\begin{matrix}{\beta = {{\pm \frac{3}{2}}\pi}} & {{Equation}\quad 7}\end{matrix}$

[0075] From Equation 1, the optimal angle between distance r and thecenter axis of the socket, denoted θ_(fix)|_(optimal), is defined as:$\begin{matrix}{\left. \theta_{fix} \right|_{optimal} = {\begin{bmatrix}{{+ \pi}/2} \\{{- \pi}/2}\end{bmatrix} - \theta_{k} - \alpha}} & {{Equation}\quad 8}\end{matrix}$

[0076] where +π/2 and −π/2 correspond to the rear and the front actuatorconfiguration respectively.

[0077] The result is that the optimal angle θ_(fix) is preferably set at125±3 degrees.

What is claimed is:
 1. An actuated leg prosthesis for above-kneeamputees, the prosthesis comprising: a knee member; first means forconnecting a socket over the knee member; an elongated trans-tibialmember having an upper end and a bottom end, the trans-tibial memberdefining a main longitudinal axis; second means for connecting anartificial foot under the bottom end of the trans-tibial member; alinear actuator having an upper end and a bottom end; third means foroperatively connecting the trans-tibial member to the knee member;fourth means for operatively connecting the upper end of the actuator tothe knee member; and fifth means for operatively connecting the bottomend of the actuator to the bottom end of the trans-tibial member.
 2. Theprosthesis according to claim 1, wherein: the third means comprise afirst pivot assembly defining a first pivot axis that is perpendicularto the main longitudinal axis; the fourth means comprise a second pivotassembly defining a second pivot axis that is substantially parallel tothe first pivot axis, the second pivot axis being spaced apart from thefirst pivot axis and the main longitudinal axis; and the fifth meanscomprise a third pivot assembly defining a third pivot axis that issubstantially parallel to and spaced apart from the first pivot axis. 3.The prosthesis according to claim 1, wherein the trans-tibial member hasa middle section comprising at least two spaced-apart bars, the barsgenerally defining a space in which most of the actuator is located. 4.The prosthesis according to claim 1, further comprising an artificialfoot attached under the bottom end of the trans-tibial member, theartificial foot defining a front side and a rear side of the prosthesis.5. The prosthesis according to claim 4, wherein the upper end of theactuator is connected to the front side of the prosthesis.
 6. Theprosthesis according to claim 5, wherein the trans-tibial membercomprises a back plate extending between the upper end and the bottomend of the trans-tibial member.
 7. The prosthesis according to claim 4,wherein the upper end of the actuator is connected to the rear side ofthe prosthesis.
 8. The prosthesis according to claim 7, wherein thetrans-tibial member has a middle section comprising at least twospaced-apart bars, the bars generally defining a space in which most ofthe actuator is located.
 9. The prosthesis according to claim 4, furthercomprising a socket attached over the knee member.
 10. The prosthesisaccording to claim 1, further comprising sixth means for controlling theactuator.
 11. The prosthesis according to claim 10, wherein the sixthmeans comprise a controller outputting control signals in response toinput signals from proprioceptors.
 12. The prosthesis according to claim11, wherein the controller has an output connected to a power drive, thepower drive supplying electrical energy to the actuator, coming from apower source, in response to the control signals.
 13. The prosthesisaccording to claim 11, wherein the input signals further comprisesignals from sensors mounted the prosthesis and located outside theprosthesis.
 14. An actuated leg prosthesis for above-knee amputees, theprosthesis comprising: a knee member; a socket connected over the kneemember; an elongated trans-tibial member having an upper end and abottom end, the trans-tibial member defining a main longitudinal axis;an artificial foot connected under the bottom end of the trans-tibialmember, the artificial foot defining a front side and a rear side of theprosthesis; a linear actuator having an upper end and a bottom end; afirst pivot assembly to operatively connect the trans-tibial member tothe knee member, the first pivot assembly defining a first pivot axisthat is perpendicular to the main longitudinal axis; a second pivotassembly to operatively connect the upper end of the actuator to theknee member, the second pivot assembly defining a second pivot axis thatis substantially parallel to the first pivot axis, the second pivot axisbeing spaced apart from the first pivot axis and the main longitudinalaxis; and a third pivot assembly to operatively connect the bottom endof the actuator to the bottom end of the trans-tibial member, the thirdpivot assembly defining a third pivot axis that is substantiallyparallel to and spaced apart from the first pivot axis.
 15. Theprosthesis according to claim 14, wherein the trans-tibial member has amiddle section comprising at least two spaced-apart bars, the barsgenerally defining a space in which most of the actuator is located. 16.The prosthesis according to claim 14, wherein the upper end of theactuator is connected to the front side of the prosthesis.
 17. Theprosthesis according to claim 16, wherein the trans-tibial membercomprises a back plate extending between the upper end and the bottomend of the trans-tibial member.
 18. The prosthesis according to claim14, wherein the upper end of the actuator is connected to the rear sideof the prosthesis.
 19. The prosthesis according to claim 18, wherein thetrans-tibial member has a middle section comprising at least twospaced-apart bars, the bars generally defining a space in which most ofthe actuator is located.
 20. The prosthesis according to claim 14,further comprising a controller to control the actuator, the controlleroutputting control signals in response to input signals fromproprioceptors.
 21. The prosthesis according to claim 20, wherein thecontroller has an output connected to a power drive, the power drivesupplying electrical energy to the actuator, coming from a power source,in response to the control signals.
 22. The prosthesis according toclaim 20, wherein the input signals further comprise signals fromsensors mounted the prosthesis and located outside the prosthesis.